A silica aerogel is an ultra-porous material in which nano-sized silica (SiO2) particles form a three-dimensional network structure and which has a porosity of 95% or more. Thus, the silica aerogel may be effectively applied to various fields including thermal insulation materials, moisture absorbents, various carriers, low-dielectric coating films, anti-reflection films, and the like because the silica aerogel has very high porosity, specific surface area, and pore volume and very low thermal conductivity, dielectric constant, refractive index, and the like.
Generally, the silica aerogel may be prepared in monolithic and powdery shapes. When the silica aerogel is in a powdery shape, the silica aerogel may be composited with fibers so that the silica aerogel is commercialized in the form of an aerogel blanket or aerogel sheet. Because the blanket or sheet has flexibility, it may be bent, folded, or cut to a predetermined size or shape. Therefore, the silica aerogel may not only be applied to industrial fields such as thermal insulation panels for liquefied natural gas (LNG) carriers, industrial thermal insulation materials, space suits, transportations and vehicles, and thermal insulation materials for power generation but may also be applied to household goods such as jackets or shoes. Further, when used in fire doors as well as roofs or floors in houses such as apartments, the silica aerogel is highly effective in preventing fire.
A silica aerogel powder may be prepared by first preparing a silica wet gel, mechanically pulverizing the silica wet gel, and then drying the pulverized silica wet gel under a super-critical or atmospheric pressure condition. However, in this case, this method has a drawback in that it is very difficult to prepare an aerogel powder having a certain size because the method includes a process of mechanically pulverizing the silica wet gel.
Also, the fine silica aerogel powder has a drawback in that handling and working properties may be severely degraded because the silica aerogel powder is very light in weight to easily form dust and has poor powder flowability. Therefore, there is an urgent demand for establishment of technology for preparing a spherical powder in a granular shape.
Korean Unexamined Patent Publication No. 10-1310286 discloses a method for preparing a spherical silica aerogel powder, which includes preparing a high-purity silica sol from a water glass solution using an ion exchange resin, and subjecting the silica sol to solvent substitution and surface modification processes. However, the invention has disadvantages in that the spherical silica aerogel powder is very expensive due to low productivity because the method essentially required the long-term solvent substitution and surface modification processes, and is not suitable for mass production because the ion exchange resin is used.
The most difficult challenges in preparing the silica aerogel powder from the water glass solution include degraded productivity due to the long solvent substitution and surface modification processes, difficulty in obtaining a powder having a uniform spherical shape, and the like.
Accordingly, the present inventors have conducted research to solve the above problems, and found a novel method for preparing a spherical silica aerogel powder having a uniform spherical shape, which is capable of reducing a process time.